The present invention relates to a composition for manufacturing a filming or film layer which is interposed between a phosphor layer and an aluminum layer when manufacturing a screen for a cathode ray tube, and to a method for manufacturing a cathode ray tube using the same.
Generally, there is provided a phosphor layer and an aluminum deposited layer on the inner surface of a panel of a cathode ray tube to form a screen.
The phosphor layer emits light when stimulated by an electron beam radiated from an electron gun. The emitted light is a scattered light and radiates to all directions including forward and backward of the panel glass. And this largely lowers the emission luminance at the front of the panel where the image is reproduced, when compared with that expected from the actually emitted light intensity from the phosphor.
To solve the above mentioned problem, a deposited metal layer is formed over the phosphor layer with a certain gap. The deposited metal layer reflects the light radiated backward from the panel to the front side, and this enhances the luminance of the image.
Most of the deposited metal layer is an aluminum deposited layer which is formed by a vacuum deposition method employing aluminum of which specific gravity is small, and so the thus formed aluminum layer can transmit electrons having high-energy with little energy loss.
The phosphor layer formed on the inner surface of the panel has an uneven surface because of the irregularity of the phosphor particle size. Accordingly, if the aluminum is deposited on the surface of the phosphor layer, an aluminum deposited layer having an uneven surface would be formed and the ratio of regular reflection of the light emitted from the phosphor would be decreased.
In order to increase the reflection effect, an even aluminum layer should be formed over the phosphor layer with a certain gap. To manufacture such an aluminum layer, an organic composition which decomposes at about 450.degree. C., is coated on the surface of the phosphor layer to make an evenly coated layer. On the surface of the coating layer, aluminum is deposited and then the coating layer is decomposed by thermolysis at about 450.degree. C. The above mentioned intermediate coating layer is called a filming or film layer.
FIG. 1 is a schematic cross sectional view of a screen before baking. On the surface of a panel 1, a phosphor layer 2 having an uneven surface is formed. And, on the surface of the phosphor layer 2, an organic filming layer 3 having a comparatively even surface is formed. The layer on the surface of the filming layer is an aluminum deposited layer 4 and ammonium oxalate 5 having needle shaped structure is protrusively embeded in the aluminum deposited layer.
The filming layer is manufactured by the two common methods described below.
First, a spin coating method using an acryl emulsion is well known as disclosed in Japanese Patent publication No. 57-18815. The spin coating method proceeds by spin coating an acryl emulsion homogeneously on the surface of the phosphor layer formed on the inner surface of the panel and decomposing the acryl emulsion particles during a drying process to obtain an even coating layer through bonding between the acryl monomers produced by the decomposition. According to this filming layer manufacturing a large amount of energy is consumed for the drying process. If the drying condition is inadequate, the acryl emulsion particles do not decompose and an evenly coated layer can not be produced, which deteriorates emission luminance. Moreover, if the filming layer is too thin, subsequently deposited aluminum permeates the phosphor layer and deteriorates emission luminance, and if the layer is too thick, the aluminum layer peels off. Therefore, additional attention to controlling the thickness of the layer is needed.
U.S. Pat. No. 3,821,009 discloses a lacquer spray method. The lacquer spray method proceeds by dissolving acrylic organic materials in hydrophobic solvent such as methyl ethyl ketone, xylene and toluene to obtain lacquer. The lacquer is sprayed on the wetted phosphor layer to make an even organic layer, forming an interface with water contained in the phosphor layer. By this method, a layer smoother than that obtained by the acryl emulsion coating method is obtained and the emission luminance of the cathode ray tube is enhanced. Because there's no drying process in this method, a large amount of energy is saved. However, the organic solvents such as xylene and toluene are explosive and flammable, so a separately enclosed space and powerful ventilator are needed. Accordingly, great expense for establishing the installation is required.